Team led by: Tetra Tech, Inc.
Our role: Hydrology Futures, LLC, in collaboration with Edwin Maurer (Santa Clara University), leads the project component concerned with climate change impacts on the hydrology of Eastern Sierra Nevada. Our expert team includes Roger Bales (Sierra Nevada Research Institute and U.C. Merced) and Norm Miller (U.C. Berkeley and U. Arizona).
Client: Los Angeles Department of Water and Power (LADWP)
Project Timeline: 2008-2011
Introduction
Precipitation from the Eastern Sierra Nevada is one of the main water sources, and the one of highest quality, for Los Angeles’ more than 4 million people. Winter precipitation is stored in the large natural reservoir that is the snowpack, and meltwater (some 200 to 500 thousand acre-feet annually) is delivered to the city in the dry season by the 340-mile long Los Angeles Aqueduct (LAA). The relative locations of the watershed, the aqueduct, and the supply area are shown in the figure below. Seven reservoirs built along the aqueduct have a combined storage capacity of about 300 thousand acre-feet. Future availability of this water supply source is of critical importance to the city’s growing population and large economy.
Traditionally water-limited, Los Angeles now faces renewed water pressures. These include a Federal Court ruling that limits exports from the Sacramento-San Joaquin Delta; the city’s commitment in the last two decades to environmental mitigation and flow enhancements in Owens Valley and Mono Lake Basin (which have reduced the aqueduct’s average contribution to the city from a historical 2/3 to about 1/3 of total); the contamination of San Fernando valley groundwater; sustained drought in the Colorado River; and finally, uncertain climate change effects that loom on the horizon.
The Mayor’s plan includes exploration of opportunities for groundwater storage along the Los Angeles Aqueduct, in the Owens Valley and the Antelope Valley; the pursuance of a groundwater conjunctive use storage project in the L.A. County groundwater basins; and the construction of a connection between the LAA and the California Aqueduct, located at their intersection point in Antelope Valley. The interconnection, whose design is nearly complete and whose construction is planned for the present year, will allow water transfers and could be used to move water for groundwater storage.
The City of Los Angeles’ dependence on snowpack for water supply is mirrored by urban centers throughout the Western United States where over 70% of annual runoff originates from snowmelt (Serreze et al., Water Resources Research vol.35 no.7, 1999). Indeed, such dependence on snowpack is shared by a full one-sixth of the world’s population (Barnett et al., Nature vol.438, 2005). This is the reason why one of the most significant potential impacts of climate change is the loss of snowpack and a shift towards earlier annual melt time.
Besides efforts at decreasing water use through conservation and reuse/recycling, development of storage infrastructure to help compensate for the loss of natural snow storage, and the development of infrastructure facilitating flexible water management are key adaptation strategies to investigate the changing hydroclimate. Given the large scale of the projects involved, the development of these alternatives demands high confidence for estimates of future climate change and snowpack response. This project entails:* Selection of the most current projections of future climate, snowmelt runoff and its timing, and water quality outcomes in LADWP’s Eastern Sierra Watershed,
* Analysis of the response of the existing surface water system connecting the Owens Valley to Los Angeles,
* Development of alternative adaptation options, and of objective evaluation criteria to compare among different options.
Footnotes:
2. Read the Mayor's Water Supply Action Plan here
3. According to the plan's May 15, 2008 press release, funding is provided by a combination of fees on industrial polluters, grants, and already budgeted LADWP funds.